Brushless motor commutation and control

ABSTRACT

A commutation apparatus drives a brushless motor having a stator equipped with a plurality of coils and a rotor. The commutation apparatus comprises a rotatable commutator shaft, two or more conducting rings carried discretely about the shaft, and two or more conducting segments carried discretely about the shaft at staggered positions along or near a plane perpendicularly intersecting the shaft. Each conducting segment is electrically connected to one of the conducting rings. Two or more electrical source contacts are provided for rotatably connecting a power supply across pairs of the conducting rings. A plurality of electrical load contacts is further provided for sequentially, rotatably connecting the conducting segments to discrete coils of the brushless motor. In particular embodiments of the commutation apparatus, a magnetic coupling is employed for rotatably coupling the commutator shaft to the rotor of the brushless motor, and a pressure-bearing container is provided for rotatably supporting the commutator shaft and the coupling therein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and is a Continuation in Part ofU.S. patent application Ser. No. 11/216,509, filed on Aug. 31, 2005,which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to apparatus and methods for brushlessmotor communication and control, and more particularly to suchcommutation and control in a downhole environment.

BACKGROUND

Electric motors are the main means by which electrical energy is changedinto mechanical energy. In industrial applications, electric motorsrange in size and power rating. There are several different types ofmotors in industrial use today. However, they can be grouped into twomain categories, namely, brush-type and brushless. Brushless motors arein general made of a stator with a stator winding, and a rotor. Therotor can be made of only laminations, as is the case with the switchedreluctance and synchronous reluctance motors. It can be made of a shaftwith magnets mounted in different configurations, as in brushlessmotors, or permanent magnet synchronous motors can be used. Or, in thegeneral case, the rotor can be combination of all the abovetechnologies.

One thing all these technologies have in common is the need for an inputvoltage with variable magnitude and frequency to control them.Typically, a three-phase inverter is used for this task, and electroniccommutation of a DC voltage is used to provide the variable voltage andfrequency. In an ideal case, the use of a brushed DC motor would haveeliminated the need to use a three-phase inverter in any application,especially ones that already have a provision for a variable DC voltage.In speed control applications, the use of a brushed DC motor would alsoeliminate the need for complex position sensing. In other cases, onewould only need a variable DC voltage to control the motor, which wouldcut down the amount of electronics, and thus increase the efficiency andreduce the cost.

However, in downhole applications, the use of brushed DC motors issimply not possible because of the difficulty in placing the motor inair and applying a rotating seal that can withstand full differentialpressure and motor torque. It is possible to magnetically couple theshaft torque of a brushed DC motor, but this is generally veryinefficient. Placing the motor in oil will also not be possible becauseof the brushes and the commutator segments on the rotor need to be incontact in order to conduct electric current. The presence of an oilfilm between these two contacts will prevent proper conduction ofcurrent, and thus inhibit torque production.

The use of brushless motors, however, has some limitations. Particulardifficulties in applying brushless motors downhole relate to theconventional use of electronic motor drives for communication andcontrol of such motors. One of the main contributors to the developmentcost of a tool can be the development of such a motor drive. This isespecially true in downhole tool development where the harshenvironmental conditions limit the application of commercially availableelectronics. Thus, it is desirable—for at least some applications—toreduce or eliminate the requirement for power conversion electronics inbrushless motor communication and control.

U.S. Pat. No. 6,239,531 to McGaughey and U.S. Pat. No. 6,667,564 to TanhM. Bui et al both present mechanical commutator solutions havingapplication in brushless motors. The '564 patent relates to anintegrated motor/commutator system that relies on a particular timingcam and conducting terminals. The '531 patent relates to anotherintegrated motor/commutator system that is characterized by a flexibleconductive ring. Patent Publication No. WO 01/50578A1 to Pengov alsodescribes a mechanical commutator, but one that is limited to driving aswitched reluctance motor.

A need therefore exists for a mechanical commutator system for abrushless motor that is adaptive to downhole applications. For example,a need exists for such a commutator system that permits the physicalseparation of the commutator from the driven motor, e.g., using magneticcouplings, so as to permit the commutator and motor to be operated indiscrete chambers or conditions.

SUMMARY

The above-described needs, problems, and deficiencies in the art, aswell as others, are addressed by the present invention in its variousaspects and embodiments. In one aspect, the present invention provides acommutation apparatus for a brushless motor having a stator equippedwith a plurality of coils and a rotor equipped with a permanent magnetassembly. The commutation apparatus comprises a rotatable commutatorshaft, two or more conducting rings carried discretely about the shaft,and two or more conducting segments carried discretely about the shaftat staggered positions along or near a plane perpendicularlyintersecting the shaft. Each conducting segment is electricallyconnected to one of the conducting rings. Two or more electrical sourcecontacts are provided for rotatably connecting a power supply acrosspairs of the conducting rings. A plurality of electrical load contactsis further provided for sequentially, rotatably connecting theconducting segments to discrete coils of the brushless motor. It will beappreciated that the inventive commutation apparatus may be employed toadvantage with any brushless motor, such as induction type, synchronousreluctance type, etc.

In particular embodiments of the commutation apparatus, a coupling isemployed for rotatably coupling the commutator shaft to the rotor of thebrushless motor. The coupling may comprise a magnetic coupling elementcarried by the commutator shaft that complements a magnetic couplingelement carried by the rotor of the brushless motor.

In particular embodiments of the commutation apparatus, a container isprovided for rotatably supporting the commutator shaft and the couplingtherein. The container may be adapted for withstanding downhole fluidpressure within a wellbore penetrating a subsurface stratum.Additionally, the container may provide a means for positioning theelectrical source and load contacts. Thus, the electrical sourcecontacts may be carried within the container about the commutator shaftfor establishing continuous electrical connections with the respectiveconducting rings. Similarly, the electrical load contacts may be carriedwithin the container about the commutator shaft for establishingstaggered electrical connections with the respective conducting segmentsalong or near the plane. Both the electrical source contacts and theelectrical load contacts may comprise spring-loaded brushes.

The number of electrical contacts are not constrained by the number ofpoles of the brushless motor. In particular embodiments, the brushlessmotor may be a two-pole motor having a commutation apparatus with twoconducting segments. It will be appreciated by those skilled in the artthat other configurations may also be suitable for establishing thedesired rotating electrical contacts, in accordance with the presentinvention. Thus, the inventive commutation apparatus may be equippedwith varying numbers of conducting segments, depending on variables suchas the available space in a tool or system. For example, although fourconducting segments may be employed to advantage for a four-pole motor,a particular embodiment may employ twelve conducting segments for afour-pole motor due to nothing more than size constraints.

The commutation apparatus may comprise two conducting rings carrieddiscretely about the commutator shaft, and two conducting segmentscarried discretely about the commutator shaft at staggered positionsalong or near a plane perpendicularly intersecting the commutator shaft.Each conducting segment is electrically connected to one of theconducting rings. Two electrical source contacts are employed forrotatably connecting a power supply across the conducting rings. Sixelectrical load contacts are employed for sequentially, rotatablyconnecting the two conducting segments to two discrete coils of thebrushless motor.

By way of further example, in other embodiments, the commutationapparatus may employ five conducting rings carried discretely about thecommutator shaft, and four sets of four conducting segments carrieddiscretely about the commutator shaft at staggered positions along ornear four respective planes perpendicularly intersecting the commutatorshaft. Each conducting segment is electrically connected to one of theconducting rings. Twelve electrical source contacts may be employed forrotatably connecting a power supply across pairs of the conductingrings, and twelve electrical load contacts may be employed forsequentially, rotatably connecting pairs of the conducting segments totwo or more discrete coils of the brushless motor.

In another aspect, the present invention provides a commutated DC motorassembly, comprising a brushless motor having a stator equipped with aplurality of coils and a rotor equipped with a permanent magnetassembly. A commutator shaft is rotatably carried in axial alignmentwith the rotor. Two or more conducting rings are carried discretelyabout the commutator shaft, and two or more conducting segments arecarried discretely about the commutator shaft at staggered positionsalong or near a plane perpendicularly intersecting the shaft. Eachconducting segment is electrically connected to one of the conductingrings. Two or more electrical source contacts are employed for rotatablyconnecting a power supply across pairs of the conducting rings. Aplurality of electrical load contacts are employed for sequentially,rotatably connecting the conducting segments to discrete coils of thebrushless motor. An assembly is further employed for rotatably couplingthe rotor of the brushless motor to the commutator shaft. The couplingassembly may comprise complementing magnetic coupling elements carriedrespectively by the commutator shaft and the rotor of the brushlessmotor.

Particular embodiments of the commutated DC motor assembly furthercomprise a container for rotatably supporting the commutator shaft andthe coupling therein. The container may be adapted for withstandingdownhole fluid pressure within a wellbore penetrating a subsurfacestratum. The electrical source contacts may comprise spring-loadedbrushes carried within the container about the commutator shaft forestablishing continuous electrical connections with the respectiveconducting rings. Similarly, the electrical load contacts may comprisespring-loaded brushes carried within the container about the commutatorshaft for establishing staggered electrical connections with therespective conducting segments along or near the plane.

In a further aspect, the present invention provides a method forcommutating a brushless motor having a stator equipped with a pluralityof coils and a rotor equipped with a permanent magnet assembly. Themethod comprises the steps of applying a current source across two ormore discretely-carried conducting rings of a rotatable commutatorshaft, with the conducting rings having two or more conducting segmentselectrically connected thereto. The commutator shaft is rotatablycoupled to the rotor of the brushless motor. The conducting segments aresequentially connected to discrete coils of the brushless motor usingrotation of the commutator shaft so as to sequentially energize thecoils of the stator. The commutator shaft may be rotatably coupled tothe rotor of the brushless motor using complementing magnetic couplingelements. The conducting segments may be sequentially connected todiscrete coils of the brushless motor by rotatably supporting thecommutator shaft within a container having a peripheral arrangement ofelectrical load contacts that are electrically connected to the coils ofthe stator.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the above recited features and advantages of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference to theembodiments thereof that are illustrated in the appended drawings. It isto be noted, however, that the appended drawings illustrate only typicalembodiments of this invention and are therefore not to be consideredlimiting of its scope, for the invention may admit to other equallyeffective embodiments.

FIG. 1 is a schematic representation of a conventional brushed DC motor.

FIGS. 2A-2B schematically illustrate the operating principle of thebrushed DC motor of FIG. 1.

FIGS. 3A-3B schematically illustrate the production of alternatingcurrent in a simple circuit.

FIGS. 3C-3D illustrate equivalent circuit diagrams for respective FIGS.3A-3B.

FIGS. 4A-4F are sequential current flow diagrams through the coilwindings (“coils”) of a stator of a brushless motor.

FIG. 5 is a schematic representation of a conventional electroniccommutation apparatus using an inverter.

FIG. 6 is a schematic representation of a conventional brushless motoremploying Hall sensors to complement an electronic commutation apparatuslike that shown in FIG. 5.

FIG. 7 is a schematic representation of one embodiment of a mechanicalcommutator employing a commutator shaft according to the presentinvention.

FIG. 8 is a detailed perspective view of the conducting ring andconducting segments of the commutator shown in FIG. 7.

FIG. 9 is a schematic representation of an assembly wherein thecommutator of FIG. 7 is rotatably coupled to a brushless motor using amagnetic coupling.

FIG. 10 is a wiring diagram of the commutator-motor assembly of FIG. 9,with the conducting rings and conducting segments shown “unrolled” fromthe commutator shaft.

FIG. 11 is a perspective view of an alternative commutator shaftcompared to the commutator shaft employed in FIGS. 7 and 9.

FIG. 12 is a perspective view of a commutator housing that complementsthe commutator shaft of FIG. 11.

FIG. 13 is a cross-sectional view of the commutator housing, taken alongsection line 13-13 of FIG. 12.

FIG. 14 is a schematic representation of the conducting rings andconducting segments of the commutator shaft of FIG. 11, shown “unrolled”from the shaft, along with the overlying positions of electrical source(power) brushes and electrical load (stator coil) brushes of thecommutator housing of FIG. 12.

FIG. 15 is a side view of a downhole borehole inspection tool having acommutator-motor assembly according to one embodiment of the presentinvention.

FIG. 16 is a side view of a downhole casing inspection tool having acommutator-motor assembly according to one embodiment of the presentinvention.

FIG. 17 is a side view of a tool having a commutator-motor assemblyaccording to one embodiment of the present invention, wherein the toolmay be used as a downhole fluid sampling tool and/or a downholeformation pressure measurement tool.

FIG. 18 is a side view of a downhole formation sampling tool having acommutator-motor assembly according to one embodiment of the presentinvention.

FIG. 19 is a side view of a downhole casing driller tool having acommutator-motor assembly according to one embodiment of the presentinvention.

FIG. 20 is a side view of a downhole mechanical services tool having acommutator-motor assembly according to one embodiment of the presentinvention.

FIG. 21 is a side view of a downhole rotary steerable tool having acommutator-motor assembly according to one embodiment of the presentinvention.

FIG. 22 is a side view of an electrical submersible pump having acommutator-motor assembly according to one embodiment of the presentinvention.

FIG. 23 is a side view of a flow control device having acommutator-motor assembly according to one embodiment of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In order to appreciate the invention at hand, it is useful to summarizethe theory of operation of brushed DC motors. FIG. 1 shows a simplifieddrawing illustrating the operating principles of a brushed DC motor andthe main functions of its components. This simplified drawing shows twostationary electrical contacts, such as brushes b₁ and b₂, connected toa current source supplying current i_(a). The brushes b₁, b₂ are placedagainst respective semi-cylindrical commutator segments s₁ and s₂. FIG.1 also depicts a coil winding (“coil”), labeled as 1-1 b-1′, connectedto the segments s₁ and s₂ and placed in a magnetic field Ø_(f) createdby the permanent magnets labeled simply as N, S.

FIGS. 2A-2B show the motor of FIG. 1 in sequential end views to clarifythe motor's operation. In the illustrated position of FIG. 2A, currentwill pass from the current source i_(a) into brush b₁ and segment s₁into side 1 of the coil and then back through side 1′ and segment s₂ andbrush b₂. Due to the current passing in a conductor (i.e., the coil)placed in a magnetic field (the field Ø_(f)), a force will develop onthe coil. Each side of the coil, 1 and 1′, will then have a forcedeveloped that is opposing the force of the other side in direction. Thepresence of the two opposing forces will then produce a torque T_(em),which will in turn cause the rotor R to rotate as indicated by ω_(m).

FIG. 2B illustrates the rotation of the rotor R to a new state,resulting from the positive current flowing in side 1 on the left (asseen in FIG. 2A) and the corresponding torque applied to the rotor.Thus, side 1′ (on the right in FIG. 2A) is now on the left in FIG. 2Band is carrying the positive current. Thus, the brushes b₁ and b₂ act asa means to flip the current in the proper winding (i.e., coil sides 1,1′).

FIGS. 3A-3B show an example of the application of brushes to produce analternating current in a simple R-L load. These figures complement theabove summary of the operation of a brushless motor to complete thereader's understanding of the invention at hand. FIG. 3A shows twosemicircular segments 10, 12 having small insulating layers 11 betweenthem. The top (outer surface) of each of the segments 10, 12 isconducting. Stationary brushes 14, 16, 18, 20 are placed in a particularpattern around the segments. The equivalent circuit of the system ofFIG. 3A is shown in FIG. 3C, where an R-L load and power source areconnected in a certain configuration due to the brushes and theircontact with the segment conducting surfaces. If the semicircularsegments 10, 12 are rotated 90° as shown in FIG. 3B, another equivalentcircuit will be created (see FIG. 3D). The geometry of the brushes,combined with the rotation of the segments, therefore acts as aswitching means for the circuit. The means of rotation of the segmentsin this case is not significant to the explanation. Because this is asimple R-L load, the rotation will need to be applied using an externalmeans.

FIGS. 4A-4F present the current flow diagrams required for continuoustorque production in a conventional brushless DC motor, represented bystator coil windings (“coils”) A, B, C. It can be seen that at eachmoment in time the current will be flowing between two terminals or intwo phases (coils), followed by a sequence of current switching eventsso as to energize different pairs of terminals/phases. Thus, theswitching sequence from FIG. 4A to FIG. 4F progresses so as to energizestator coil pairs as follows: AC, AB, CB, CA, BA, BC. If current were toflow sequentially in these patterns, torque would be continuouslyproduced in the motor and continuous rotation of the motor's rotor wouldoccur.

This selective current flow switching is conventionally accomplishedusing an electronic inverter as shown schematically in FIG. 5, whereHall sensors Hall A, Hall B, Hall C are employed to indicate thebeginning and end of each of the six current flow paths shown in FIGS.4A-4F. A controller sends the proper signals to an IGBT driver toconnect the appropriate stator phases A, B, C to the DC rail, thusforcing current into the desired phases.

FIG. 6 is a schematic representation of a conventional brushless motor Mhaving three stator coils SC distributed about a rotatable rotor R. Therotor drives Hall sensor magnets HSM into/through the positions of whichare sensed by the Hall sensors (A, B, C) of an electronic commutationlike that shown in FIG. 5.

The present invention aims to eliminate the need for such electronicthree-phase inversion. This is possible in applications requiring aconstant speed, or where speed can be varied by merely changing theinput DC voltage.

FIG. 7 is a schematic representation of one embodiment of a mechanicalcommutator 710, also known as a commutation apparatus, according to thepresent invention. The commutation apparatus 710 comprises a commutatorshaft 712 carried for rotation within a housing or container 714 adaptedto withstand the pressures and temperatures of downhole applications.Such a container can be charged with air (as opposed to oil, forexample) as part of a downhole tool that utilizes a brushless motor. Theshaft 712 is supported by a bearing assembly, referenced as 716, whichincludes radial and/or thrust bearings as are generally known in theart.

A coupling element, in particular an element 740 of a magnetic couplingassembly, is carried by the commutator shaft 712 for rotatably couplingthe commutator shaft to the rotor of a driven brushless motor (not shownin FIG. 7). Thus, the magnetic coupling element 740 may be used tocomplement a corresponding magnetic coupling element carried by therotor of the brushless motor, in a manner that is described below. Itwill be appreciated the element 740 may be similar or identical to thatpreviously used for Hall sensing (see Hall sensor magnet HSM in FIG. 6).

With reference now to FIGS. 7 and 8, two or more conducting strips orrings 718 are carried discretely about the shaft 712, such that there isno electrical contact between the conducting rings 718. Thus, aninsulating material (see material section 719 in FIG. 8) may be disposedbetween the rings 718 or the outer surface of the shaft 712 may benonconductive, as is known in the art. It will be appreciated that theconducting rings may be implemented in varying numbers and with variousconducting patterns (other strip configurations are described below) toprovide for mechanical commutation of a brushless motor according to thepresent invention.

Two conducting segments 720 are carried discretely about the shaft 712at staggered positions 180° apart along or near a plane (see plane P inFIG. 7) perpendicularly intersecting the shaft 712. Each conductingsegment 720 is electrically connected to one of the conducting rings718.

Two or more electrical source contacts, in particular brushes 722, areprovided for rotatably connecting a power supply PS (e.g., a batterybank or other source) across the pair of conducting rings 720. Leads 726extend from the power supply to pick-ups 724 carried on the outersurface of the container 714. Leads 727 extend from the pickups 724 tothe brushes 722, which are spring loaded by springs 728 to ensurecontact between the brushes 722 and the conducting rings 718.

With reference now to FIGS. 7 and 10, a plurality of electrical loadcontacts, in particular six brushes 730 (only two being shown in FIG.7), is further provided for sequentially, rotatably connecting theconducting segments 720 to discrete stator coils SC (individuallyreferenced as A, B, C in FIG. 10) of a driven brushless motor 900. Leads732 extend from pick-ups 734 carried on the outer surface of thecontainer 714 to the stator coils SC. Leads 736 extend from the pickups734 to the brushes 730, which are spring loaded by springs 738 to ensurecontact between the brushes 730 and the conducting segments 720. In thismanner, each of the conducting segments 720 is connected to acorresponding terminal (+ or −) of the power supply PS through thecontainer 714 and the system of leads, pick-ups, and brushes. Thecontainer 714 provides a means for positioning the electrical source andload brushes 722, 730. Thus, with particular reference to FIG. 10(described further below), at any instant in time two of the loadbrushes 730 are connected to the two conducting segments 720, therebyselectively connecting the power supply terminals to particular statorcoils SC of the driven brushless motor.

FIG. 9 is a schematic representation of an assembly wherein thecommutator 710 of FIG. 7 is rotatably coupled to a brushless motor 900using a magnetic coupling assembly 902. In one embodiment, thecommutator 710 employs a rotating ring/segment and brush assembly thatis isolated in air within the container 714, as described above. Thebrushless motor 900 has a stator 910 equipped with a plurality of coilsSC and a rotor 912 equipped with a permanent magnet assembly (indicatedby poles N, S). The commutator shaft 712 is rotatably carried by thecontainer 714 in axial alignment with the rotor 912 and a shaft 920connected to the rotor. The magnetic coupling assembly 902 rotatablycouples the rotor shaft 920 of the brushless motor to the commutatorshaft 712. The coupling assembly 902 may comprise complementing magneticcoupling elements 740, 940 (see opposing poles N, S) carriedrespectively by the commutator shaft 712 and the rotor shaft 920. Itwill be appreciated, however, that the brushes and rotating ring/segmentassembly of the commutator 710 can otherwise be located in a commoncontainer with the motor 900, in which case the commutator shaft 712could be mechanically coupled to the rotor shaft 920 without the needfor a magnetic coupling.

FIG. 10, which was briefly described above, is a wiring diagram of thecommutator-motor assembly of FIG. 9, with the conducting rings 718 andconducting segments 720 shown “unrolled” from the commutator shaft 712.In the position shown, the positive terminal of the power supply PS isconnected to a particular conducting ring 718 a via a particular pick-up724 a. The conducting segment 720 a extending from the ring 718 a isconnected to a lead c-c due to the segment 720 a being aligned with aload brush 730 e at one of the ends of the lead c-c. Lead c-c is one ofthree leads (the others being leads a-a and b-b) that extend through awall of the container 714 between the commutation apparatus 710 and themotor 900. The leads extend through the container wall in such a way(e.g., with potting) as to secure the pressure-bearing characteristicsof the container 714, as is known in the art. Lead c-c is electricallyconnected to the stator coil C, which is also connected to coils A and Bwithin the stator 910. Stator coil A is also connected to lead a-a whichterminates in a brush 730 b at one of its ends. The brush 730 b isaligned with the conducting segment 720 b, which is connected to theconducting strip 718 b. Strip 718 b is in turn connected to the negativeterminal of the power supply PS by way of pickup 724 b. In this manner,current from the power supply PS will flow through stator coils C and A,when the commutator segments 720 are positioned as shown in FIG. 10.

Such imbalanced current flow (coil B is not energized) produces torquebetween the energized coils C and A and the rotor 912, resulting inrotation of the rotor 912 and connected shaft 920. Shaft 920 has a firstend 920 a that is connected to the magnetic coupling element 940, whichis positioned adjacent the commutator's magnetic coupling element 740.The torque applied to the rotor 912 thereby produces equivalent rotationof the motor shaft 920 and the commutator shaft 712. Very little powerwill be lost in the transfer of torque from the motor shaft 920 to thecommutator shaft 712, as the lossy components are limited to the bearinglosses, friction produced by brushes rubbing against the conductingsegments, and the electrical losses in the brushes.

The coupling-induced rotation of the commutator shaft 712 causes theconducting segments 720 a, 720 b to engage another pair of load brushes730, thereby energizing coils C and B and creating further torque androtation of shafts 920, 712. This cycle of energizing stator coil pairs,creating torque, and rotating output shafts is repeated continuouslywhile the commutator conducting rings 718 are connected across the powersupply PS. The commutator 710 therefore electrically engages the stator910 while it magnetically (or mechanically) engages the rotor 912 tofulfill the commutation function. Accordingly, the stator coils will beenergized according to the following sequence: CA, CB, AB, AC, BC, BA(with the first coil being connected to the positive terminal and thesecond coil being connected to the negative terminal of the power supplyPS).

FIG. 11 is a perspective view of an alternative commutator shaft 1112compared to the commutator shaft employed in FIGS. 7 and 9. FIGS. 12-13are perspective and cross-sectional views view of a cylindricalcommutator housing 1114 that complements the commutator shaft 1112 ofFIG. 11. The commutator shaft 1112 is carried for rotation within thecontainer 1114, which is preferably adapted to withstand the pressuresand temperatures of downhole applications. As in the case of container714 described above, the container 1114 can be charged with air (asopposed to oil, for example) as part of a downhole tool that utilizes abrushless motor. The shaft 1112 may be supported by a bearing assembly(not shown) which includes radial and/or thrust bearings as aregenerally known in the art. The shaft may also be equipped with amagnetic coupling element (not shown) in similar fashion to the magneticcoupling element 740 described above.

The container 1114 is further equipped for supporting pluralities ofpower and load contacts, in particular brushes, about the shaft 1112(when the shaft is positioned within the container). With reference nowto FIG. 13, twelve brush carriers 1301-1312 are distributed about aninner cylindrical boundary 1320 of the container 1114 so as to place thecarried brushes into physical contract with the commutator shaft 1112.The brush carriers 1301-1312 are distributed such that four sets ofthree brush carriers each at least partially align with four respectiveinsulating rings 1119 (described below).The brush carriers 1303, 1307,1311 are shown in FIG. 13 as being carried generally in a common planeby respective carrier arms 1313, 1317, 1321, although one arm 1317 andits brush carrier 1307 are slightly recessed with a channel 1330 for areason that will be made clear in the description that follows.

FIG. 14 is a schematic representation of the conducting rings andconducting segments of the commutator shaft of FIG. 11, shown “unrolled”from the shaft, along with the overlying positions of electrical source(power) brushes and electrical load (stator coil) brushes of thecommutator housing of FIGS. 12-13. Five conducting strips or rings 1118a-e are carried discretely about the shaft 1112. The conducting ringsare separated by the insulating rings 1119 such that there is noelectrical contact between the conducting rings. It will be appreciatedthat the conducting rings may be implemented in varying numbers and withvarious conducting patterns other than described herein to provide formechanical commutation of a brushless motor.

Sixteen conducting segments 1120 a ₁₋₂, 1120 b ₁₋₄, 1120 c ₁₋₄, 1120 d₁₋₄, and 1120 e ₁₋₂ are carried discretely about the shaft 1112 andarranged in staggered positions 90° apart along or near four respectiveplanes (see planes P1-P4 in FIG. 14) perpendicularly intersecting theshaft 1112. Each conducting segment is electrically connected to one ofthe conducting rings.

Twelve electrical source contacts, in particular brushes, are providedfor rotatably connecting a power supply (not shown) across pairs of theconducting rings. Twelve electrical load contacts, in particularbrushes, are further provided for sequentially, rotatably connecting theconducting segments to discrete stator coils A, B, C of a drivenbrushless motor 900 (see FIG. 10). The electrical source brushes andload brushes are carried for convenience and efficiency within container1114 in twelve discrete brush carriers 1301-1312, as mentioned above.Thus, e.g., as shown particularly in FIG. 14, one source brush 1305 d iscarried with a load brush 1305 a in the brush carrier 1305, although thetwo brushes are electrically isolated from one another (nocross-conduction within the carrier).

The commutator-motor assembly of FIGS. 11-14 further employs leads,pick-ups, etc. in similar fashion to that described above in referenceto the embodiment of FIGS. 7-10, so that each of the twelve load brushesis electrically connected to one of the three stator coils A, B, C ofthe motor 900 (see FIG. 10). At any instant in time, one of theconducting segments 1120 x of a conducting ring 1118 x is placed incontact with one of the load brushes, thereby selectively connecting thepower supply terminals to two particular stator coils of the drivenbrushless motor 900.

More particularly, in the commutator position shown in FIG. 14,conducting rings 1118 a, 1118 c, and 1118 e are each connected to thepositive terminal of a power supply (not shown), while conducting rings1118 b and 1118 d are each connected to the negative terminal of thepower supply. Neither of the conducting segments (1120 a ₁₋₂) connectedto the conducting ring 1118 a is placed in contact with one of the loadbrushes, so ring 1118 a is not used at this instant to energize any ofthe stator coils. Conducting ring 1118 b has four conducting segments(1120 b ₁₋₄) connected thereto, and one of these segments, segment 1120b ₁, is placed in contact with a load brush 1309 c. Load brush 1309 c(along with the other “c” load brushes) is connected to the stator coilC of the motor 900, thereby placing the negative terminal of the powersupply in electrical connection with stator coil C. Conducting ring 1118c has four conducting segments (1120 c ₁₋₄) connected thereto, and oneof these segments, segment 1120 c ₃, is placed in contact with a loadbrush 1312 a. Load brush 1312 a (along with the other “a” load brushes)is connected to the stator coil A of the motor 900, thereby placing thepositive terminal of the power supply in electrical connection withstator coil A. Accordingly, stator coils C and A are energized,resulting in the application of torque to the rotor 912 and thecommutator shaft 1112 via a magnetic coupling assembly (not shown), insimilar fashion to that described above.

Conducting ring 1118 d has four conducting segments (1120 d ₁₋₄)connected thereto, and one of these segments, segment 1120 d ₃, isplaced in contact with a load brush 1303 c. Load brush 1303 c (like theother “c” load brushes) is connected to the stator coil C of the motor900, thereby (also) placing the negative terminal of the power supply inelectrical connection with stator coil C. Conducting ring 1118 e has twoconducting segments (1120 e ₁₋₂) connected thereto, and one of thesesegments, segment 1120 e ₁, is placed in contact with a load brush 1306a. Load brush 1306 a (like the other “a” load brushes) is connected tothe stator coil A of the motor 900, thereby (also) placing the positiveterminal of the power supply in electrical connection with stator coilA. Accordingly, stator coils C and A are further energized, primarilyfor redundancy.

It will be appreciated by those having ordinary skill in the art that atany instant four of the five conducting rings 1118 a-e will each beplaced in contact with one or more of the source brushes so as toconnect two of the rings to the positive terminal of the power supplyand two of the rings to the negative terminal of the power supply. Theconducting segments attached to the four energized conducting rings willbe placed in contact with the load brushes corresponding (redundantly)to two of the three stator coils of the motor 900. The coils will beenergized according to the following sequence: AC (described above), BC,BA, CA, CB, AB (with the first coil being connected to the positiveterminal and the second coil being connected to the negative terminal ofthe power supply PS).

The number of electrical contacts is not constrained by the number ofpoles of the brushless motor. One embodiment comprises a two-polebrushless motor (like motor 900) having a commutation apparatus with twoconducting segments. However, the inventive commutation apparatus may beequipped with varying numbers of conducting segments, depending onvariables such as the available space in a tool or system. For example,although four conducting segments may be employed to advantage for afour-pole motor, a particular embodiment may employ twelve conductingsegments for a four-pole motor due to nothing more than sizeconstraints. Other suitably-driven motor configurations will be apparentto those having ordinary skill in the art. Also, pluralities ofcommutators may be operatively connected to drive a single motor.

It will be further appreciated that the commutator and commutator-motorassembly described herein has utility in numerous downhole applications,including high temperature and pressure conditions, that requirebrushless motors. For example, FIGS. 15-23 each show exemplary tools inwhich any one of the above described commutator and commutator-motorassemblies of the present invention may be used.

FIG. 15 shows a downhole borehole inspection tool 1500 having acommutator-motor assembly 100 according to any one of the abovedescribed embodiments of the present invention. FIG. 16 shows a downholecasing inspection tool 1600 having the commutator-motor assembly 100.FIG. 17 shows a tool 1700 having the commutator-motor assembly 100,which can be used as a downhole fluid sampling and/or a downholeformation pressure measurement tool. FIG. 18 shows a downhole formationsampling tool 1800 having the commutator-motor assembly 100. FIG. 19shows a downhole casing driller tool 1900 having the commutator-motorassembly 100. FIG. 20 shows a downhole mechanical services tool 2000having the commutator-motor assembly 100. FIG. 21 shows a downholerotary steerable tool 2100 having the commutator-motor assembly 100.FIG. 22 shows an electrical submersible pump 2200 having thecommutator-motor assembly 100. FIG. 23 shows a flow control device 2300having the commutator-motor assembly 100.

Although FIGS. 15-23 show specific uses for the inventivecommutator-motor assembly, in other embodiments the commutator motorassembly may be used in any appropriate device for performing anyappropriate task. In addition, it will be understood from the foregoingdescription that various other modifications and changes may be made inthe preferred and alternative embodiments of the present inventionwithout departing from the principle, and scope of this invention. Thus,e.g., while electrical brushes are described herein for use aselectrical source and load contacts, the present invention is not solimited. Other electrical contact solutions may be apparent to thoseskilled in the art.

This description is intended for purposes of illustration only andshould not be construed in a limiting sense. The scope of this inventionshould be determined only by the language of the claims that follow. Theterm “comprising” within the claims is intended to mean “including atleast” such that the recited listing of elements in a claim are an openset or group. Similarly, the terms “containing,” having,” and“including” are all intended to mean an open set or group of elements.“A,” “an” and other singular terms are intended to include the pluralforms thereof unless specifically excluded.

1. A downhole tool comprising: a commutation apparatus for a brushlessmotor having a stator equipped with a plurality of coils and a rotorequipped with a permanent magnet assembly, the commutation apparatuscomprising: a rotatable commutator shaft; two or more conducting ringscarried discretely about the shaft; two or more conducting segmentscarried discretely about the shaft at staggered positions along or neara plane perpendicularly intersecting the shaft, each conducting segmentbeing electrically connected to one of the conducting rings; two or moreelectrical source contacts for rotatably connecting a power supplyacross pairs of the conducting rings; and a plurality of electrical loadcontacts for sequentially, rotatably connecting the conducting segmentsto discrete coils of the brushless motor.
 2. The downhole tool of claim1, further comprising a coupling at least partially carried by thecommutator shaft for rotatably coupling the commutator shaft to therotor of the brushless motor.
 3. The downhole tool of claim 2, whereinthe coupling comprises a magnetic coupling element carried by thecommutator shaft that complements a magnetic coupling element carried bythe rotor of the brushless motor.
 4. The downhole tool of claim 2,further comprising a container for rotatably supporting the commutatorshaft and the coupling therein.
 5. The downhole tool of claim 4, whereinthe container is adapted for withstanding downhole fluid pressure withina wellbore penetrating a subsurface stratum.
 6. The downhole tool ofclaim 4, wherein the electrical source contacts comprise spring-loadedbrushes carried within the container about the commutator shaft forestablishing continuous electrical connections with the respectiveconducting rings.
 7. The downhole tool of claim 4, wherein theelectrical load contacts comprise spring-loaded brushes carried withinthe container about the commutator shaft for establishing staggeredelectrical connections with the respective conducting segments along ornear the plane.
 8. The downhole tool of claim 1, wherein the brushlessmotor is a two-pole motor.
 9. The downhole tool of claim 8, comprising:two conducting rings carried discretely about the commutator shaft; twoconducting segments carried discretely about the commutator shaft atstaggered positions along or near a plane perpendicularly intersectingthe commutator shaft, each conducting segment being electricallyconnected to one of the conducting rings; two electrical source contactsfor rotatably connecting a power supply across the conducting rings; andsix electrical load contacts for sequentially, rotatably connecting thetwo conducting segments to two discrete coils of the brushless motor.10. The downhole tool of claim 1, wherein the brushless motor is afour-pole motor.
 11. The downhole tool of claim 1, comprising: fiveconducting rings carried discretely about the commutator shaft; foursets of four conducting segments carried discretely about the commutatorshaft at staggered positions along or near four respective planesperpendicularly intersecting the commutator shaft, each conductingsegment being electrically connected to one of the conducting rings;twelve electrical source contacts for rotatably connecting a powersupply across pairs of the conducting rings; and twelve electrical loadcontacts for sequentially, rotatably connecting pairs of the conductingsegments to two or more discrete coils of the brushless motor.
 12. Thedownhole tool of claim 1, wherein the downhole tool is a boreholeinspection tool.
 13. The downhole tool of claim 1, wherein the downholetool is a casing inspection tool.
 14. The downhole tool of claim 1,wherein the downhole tool is a downhole fluid sampling tool.
 15. Thedownhole tool of claim 1, wherein the downhole tool is a downholeformation pressure measurement tool.
 16. The downhole tool of claim 1,wherein the downhole tool is a downhole formation sampling tool.
 17. Thedownhole tool of claim 1, wherein the downhole tool is a downhole casingdriller tool.
 18. The downhole tool of claim 1, wherein the downholetool is a downhole mechanical services tool.
 19. The downhole tool ofclaim 1, wherein the downhole tool is a downhole rotary steerable tool.20. The downhole tool of claim 1, wherein the downhole tool is anelectrical submersible pump.
 21. The downhole tool of claim 1, whereinthe downhole tool is a flow control device.